Optical disk, optical disk drive apparatus, and optical disk tracking method

ABSTRACT

The invention provides an optical disk medium having a recording spiral formed by connecting groove tracks and land tracks alternately, and permitting detection of a connecting point between a groove track and a land track reliably is provided, and a method of tracking the optical disk medium and an optical disk drive apparatus for driving the optical disk medium. One part of an identification signal area is shifted by a predetermined distance in one radial direction from the center of a groove, while another part of the identification signal area is shifted by the same distance in the opposite radial direction from the center of the groove. A land/groove polarity of a sector is determined by the polarity of a tracking error signal and the order of the polarities during reproduction of an identification signal.

This application is a divisional of application Ser. No. 09/556,437filed on Apr. 24, 2000, which is a divisional of application Ser. No.09/332,071, filed on Jun. 14, 1999 and issued as U.S. Pat. No. 6,201,775on Mar. 13, 2001, which is a divisional of application Ser. No.08/829,119, filed on Apr. 10, 1997 and issued as U.S. Pat. No. 6,091,699on Jul. 18, 2000, the entire contents of which are hereby incorporatedby reference and for which priority is claimed under 35 U.S.C. §120; andthis application claims priority of Application No. 8-92885 filed inJapan on Apr. 15, 1996 under 35 U.S.C. §119.

BACKGROUND OF THE INVENTION

This invention relates to an optical disk in which signals are recordedboth onto recording tracks in depressed portions formed by guide groovesand onto recording tracks on projecting portions between the guidegrooves, and to an optical disk apparatus, and an optical disk trackingmethod.

As a data recording method for a large-capacity rewritable optical disk,a land/groove recording method in which data is recorded both in guidegrooves (sometimes denoted by G) and on lands (sometimes denoted by L)to increase a recording density, has been proposed. When this method isused, the recording density can be increased because the recording trackpitch can be halved compared to an optical disk having the same groovepitch but for which this method is not used. Grooves and lands may alsobe referred to as depressed portions and projecting portions,respectively.

As a conventional land/groove recording optical disk, there is providedan optical disk shown in FIG. 13, for example. It is described inJapanese Examined Patent Publication 63-57859. As shown in FIG. 13,grooves 94 and lands 95 are formed by means of guide grooves inscribedon the substrate of the disk, and a recording film 91 is formed thereon.Recording marks 92 are formed on the recording film 91 extending both onthe grooves 94 and the lands 95. The grooves 94 and the lands 95 formcontinuous data recording tracks, respectively. A light-focused spot 93of an optical disk drive apparatus for performing data recording andreproduction onto this recording medium records or reproduces data whilescanning either of the recording tracks. With a conventional land/grooverecording format, guide grooves are continuous on a disk. Thus, each ofthe data recording tracks of the grooves 94 and the data recordingtracks of the lands 95 form a single continuous recording spiral.

A single spiral land/groove format is described next.

FIG. 14 shows the configuration of an optical disk having a format inwhich each data recording track of grooves (hereinafter also referred toas a groove track) 94 having a length corresponding to a revolution ofthe disk and each data recording track of lands (hereinafter alsoreferred to as a land track) 95 also having a length corresponding to arevolution of the disk are connected alternately to form a datarecording spiral. An example of optical disks having the format shown inFIG. 14 in which groove tracks 94 and land tracks 95 are connectedalternately to form a data recording spiral, is described in JapaneseUnexamined Patent Publication 4-38633 and Japanese Unexamined PatentPublication 6-274896. The format of such optical disks is hereinreferred to as the single spiral land/groove format or the SS-L/Gformat.

An SS-L/G format optical disk has continuous data recording tracks onthe disk, so that it is suitable for continuous data recording andreproduction. When an optical disk is used as a video file, for example,continuous data recording and reproduction is essential. However, in aconventional land/groove recording optical disk shown in FIG. 13, theland tracks 95 and the groove tracks 94 form separate data recordingspirals. Thus, when data recording or reproduction is performedcontinuously from the land tracks 95 to the groove tracks 94, forexample, it is interrupted at least at one portion of the disk due to anaccess between the land tracks 95 and the groove tracks 94. The sameinterruption occurs when data recording or reproduction is performedcontinuously from the groove tracks 94 to the land tracks 95. In orderto avoid such an interruption in the data recording or reproduction, itis necessary to provide an additional buffer memory, which raises thecost. If optical disk is of a single spiral land/groove format, no suchan additional buffer memory is necessary.

In an SS-L/G format optical disk, however, a tracking servo polaritymust be switched at every revolution of the disk. Since the detection ofthis tracking servo polarity switching point is difficult, applicationof the tracking servo is also difficult. For this reason, the SS-L/Gformat optical disk has found few practical applications. Althoughformatting an SS-L/G format optical disk is disclosed in JapaneseUnexamined Patent Publication 4-38633 and Japanese Unexamined PatentPublication 6-274896 mentioned above, nothing is disclosed about aspecific method of detecting a tracking servo polarity switching point.

ln order to apply a tracking servo to an SS-L/G format optical disk, itis necessary to accurately detect between alternating points betweenalternating groove tracks and land tracks, and to switch a trackingservo polarity to be set for tracking a groove track or a land track.Examples of methods of detecting connecting alternating pointsconnecting groove tracks and land tracks are disclosed in JapaneseUnexamined Patent Publication 6-290465 and Japanese Unexamined PatentPublication 7-57302.

In the method disclosed in Japanese Unexamined Patent Publication6-290465, depressed portions and projecting portions of a constantfrequency are provided at the connecting points between land tracks andgroove tracks. FIG. 15 shows the configuration of an optical diskrecording medium described in the above-mentioned publication. Referringto FIG. 15, the connecting points are at A1, A2, A3, B1, B2, etc.Between the connecting points next to each other either a land or agroove continues, and positional data such as a track address isrepresented by wobbling grooves.

In the method disclosed in Japanese Unexamined Patent Publication7-57302, a flat part having no grooves or a predetermined pattern ofpits are provided at the connecting points between groove tracks andland tracks. FIG. 16A and FIG. 16B show the configuration of an opticaldisk recording medium described in the above-mentioned publication. FIG.16A shows an example of a flat part provided at a connecting point,while FIG. 16B shows an example of a predetermined pattern of pits. Inthis prior art example, nothing is disclosed about positional data suchas a track address, and it can be regarded that either a groove or aland continues between the connecting points on a spiral.

Now, description is directed to a case where pit pattern data fordetecting a connecting point is provided on an optical disk in whicheach of the data recording tracks is composed of a plurality of datarecording sectors having their own identification data. In the method ofproviding identification data by wobbling grooves, no interruptingportion is present in the groove of a data recording part in onerevolution except for a connecting point. Thus, the problem of erroneousdetection of a connecting point will not arise. However, the function ofrecording data onto a sector is restricted. For instance, data recordingor reproduction in units of short sectors is difficult.

In contrast with an optical disk of the above-mentioned configuration,in the case of an optical disk such as a conventional ISOmagneto-optical disk having a format in which preformattedidentification data parts representing addresses and data recordingparts recording user data are arranged separately on data recordingtracks, if identification data and a connecting point between a grooveand a land are represented in the same recording form, the problem oferroneous detection of the connecting point will arise. In order toavoid such a problem, it is necessary to ensure discrimination betweenthe pit pattern of identification data and the pit pattern for detectinga connecting point between a groove and a land. In the example disclosedin Japanese Unexamined Patent Publication 7-57302, since the pitsequence as shown in FIG. 16B is provided only at connecting points, theproblem of erroneous detection of the connecting point will not occur.However, when identification data is preformatted with a pit patternsimilar to that for detecting a connecting point and arranged in a datarecording track, it is necessary to reproduce the pit data in theconnecting point with precise pit synchronization so as to detect theconnecting point with a high reliability. This applies to all caseswhere a connecting point is detected according to the pit pattern,regardless of how the connecting point is represented, such as by meansof a pit pattern of a constant frequency or a predetermined pit pattern.

In order to reproduce pit data with precise pit synchronization,establishment of stable tracking is a prerequisite. This means that aconnecting point between a groove and a land should be correctlydetected and tracking should be switched accordingly. In order to dothis, it is necessary to distinguish between the pit pattern fordetecting the connecting point and the pit pattern for theidentification data and to reproduce the pit data for the connectingpoint with the precise pit synchronization. This falls into a circulardependency. It indicates that, according to the prior art, in an opticaldisk having a format in which each of the data recording tracks iscomposed of a plurality of track sectors having a preformattedidentification part and a data recording part arranged separately,reliable detection of a connecting point between a groove and a landwhich is essential for implementing a single spiral land/groove formatis difficult.

Now, a method of inserting identification signal prepits which has beenproposed for a conventional land/groove recording optical disk isdescribed. In the conventional land/groove recording method, threemethods of inserting identification signal prepits as shown in FIG. 17Ato FIG. 17C are known. In the method illustrated in FIG. 17A, alsoreferred to as a land/groove individual addressing method, each of landtrack sectors and groove track sectors has their own sector address. Ifthe width of prepits representing an identification signal were set tobe identical to the width of a groove, identification signal prepits ofthe adjacent track sectors would be connected, and no identificationsignal could be detected. For this reason, the width of identificationsignal prepits is set to be smaller than that of a groove, and normallyis set to be about half the width of a groove.

However, unless the diameter of a laser beam for inserting prepits ismade different from that for forming a groove during the fabrication ofa master disk in the mastering process, continuous formation of a grooveand prepits having different widths as described above cannot easily beperformed. For this reason, two separate laser beams for forming groovesand forming the prepits must be used for cutting the master disk. If twolaser beams are not aligned during the formation of grooves and prepits,there will be a tracking offset between the reproduction ofidentification signal prepits and the recording or reproduction of datarecording signals. The quality of reproduced data will thereforedeteriorate. More specifically, due to the deviation of tracking, anerror rate of the reproduced data will increase, lowering thereliability of the reproduced data. Thus, highly accurate positioning ofthe two laser beams is required, which will be a factor for raising thecost of fabrication of master disk.

In view of the above-mentioned problem, and in terms of the accuracy andthe cost of the fabrication of an optical disk, the method illustratedin FIG. 17B or FIG. 17C, capable of forming grooves and prepits with asingle laser beam is preferable. FIG. 17B and FIG. 17C respectively showthe methods capable of inserting prepits having substantially the samewidth as that of a groove.

FIG. 17B shows a conventional optical disk described in JapaneseUnexamined Patent Publication 6-176404 and which uses a method alsoreferred to as a land/groove common address method. In this method,identification signal prepits PP are disposed around the center of apair adjacent of a groove and land tracks, and the same identificationsignal prepits are shared by a groove track G and a land track Ladjacent to each other.

FIG. 17C shows a conventional optical disk described in JapaneseUnexamined Patent Publication 7-110944 and which uses a method referredto as a time-division L/G individual address method. In this method,individual addresses are provided for land tracks L and groove tracks G.The positions at which the identification signal prepits PP for theadjacent land tracks and groove tracks are arranged are shifted relativeto each other in a direction parallel to the tracks such that theidentification signal prepits do not neighbor each other.

When considering a method of providing identification signal data anddata for detecting a connecting point, immunity to defects should alsobe considered. For switching a tracking polarity by reading theidentification signal data and the data for detecting a connectingpoint, discrimination between a groove and a land should not fail in thepresence of a slight defect on the disk. It is essential to performcorrect detection of a connecting point, even if there are typicaldefects on the medium such as fine flaws, and defective holes formed ona recording film and causing reduction of index of reflection.

When considering a method of providing the identification signal dataand the data for detecting a connecting point, consideration should bealso given to a servo characteristic.

The SS-L/G format provides a higher track density because both lands andgrooves are used for recording data. However, because of this highertrack density, when a tracking offset is increased, the quality of areproduced signal deteriorates because of crosstalk from an adjacenttrack and the error rate increases due to an increase in jitter, forexample. Crosserase of data on an adjacent track, which means erasure ofpart of data on an adjacent track, may also occur during data recording.An error which will cause a tracking offset is generated due to combinedeffects of the optical head system, the arrangement of tracks in anoptical disk, and the servo systems. For this reason, such an errorgenerally has different levels for a land track and a groove track.

In order to avoid crosstalk and crosserase, different offsetcompensation is required for each of a land track and a groove track. Inthe conventional land/groove recording method, i.e., the method in whichgroove tracks and land tracks form separate data recording spirals,offset compensation can be made for the respective spirals of the landtracks or the groove tracks during the continuous tracking operation,taking a certain period. Then, after the adjustment, the amount ofcompensation can be retained. Thus, offset compensation can be achievedeasily.

With the SS-L/G format optical disk, however, tracking polarityswitching between a land track and a groove track must be made at everyrevolution of the disk. For this reason, it is necessary to maketracking offset compensation accurately and quickly. As described above,with the SS-L/G format optical disk, a method of insertingidentification signals taking account of tracking offset compensation isrequired.

The above-mentioned conventional methods of inserting identificationsignals for a land/groove recording optical disk did not provide thecharacteristics required of a SS-L/G format disk, for dealing with themedium defects or tracking offset compensation.

In the case of the land/groove common address method as illustrated inFIG. 17B, for example, identification signal prepits are disposed on oneside of a land track or a groove track. Thus, a tracking offset keepsincreasing the reproduction of identification signals. On the otherhand, in the case of the L/G individual address method as illustrated inFIG. 17C, detection of a tracking offset is difficult, which is alsotrue for the case of FIG. 17B.

The operation associated with driving an optical disk is next described.When a control system for changing the rotational speed during thedriving operation of the optical disk is used, quick and accuratedetection of a connecting point between a land and a groove will becomemore difficult. However, with an optical disk used for a videoapplication mainly requiring continuous data recording and reproduction,the above-mentioned control system should be used.

In case emphasis is placed on the compatibility with an read-onlyoptical disk, a phase-change medium is suitable as a rewritable opticaldisk. This is because, with this phase-change medium, the optical systemcan be commonly used with the read-only optical disk. However, with thephase-change medium having data recording and reproduction performancewhich can be used in practice, the range of data recording linearvelocities over which the data recording and reproduction characteristicassociated with the PWM data recording operation is satisfied is narrow.More specifically, when an optical disk is controlled with the CAV(Constant Angular Velocity), the rotational speed of the disk in theinner radial part and the rotational speed of the disk in the outerradial part will be identical, and the recording linear velocity of thedisk in the outer radial part will be approximately 2.5 to 3 timesfaster than that in the inner radial part. The currently-availablephase-change medium cannot be used over this wide range of datarecording linear velocities.

Where the rotation of the disk is CAV-controlled, if the rotationalspeed of the disk in the inner radial part is set to achieve a requireddata rate, when the outer radial part of the disk is scanned, the signalprocessing circuit must perform high speed processing nearly three timesfaster than that for the inner radial part. For this reason,implementation of the required function with hardware of a low cost willbe difficult. Further, when considering the video application of thedisk, it is preferable that the optical disk have a constant data ratebetween the outer radial part and the inner radial part.

Thus, for a rewritable optical disk used for the data recording of adigital video, because of the two reasons of the characteristic of themedium and the circuit performance, a ZCLV (Zoned Constant LinearVelocity) method is practical. In this method, an optical disk isdivided radially into a plurality of zones, and the rotational speed ofthe disk is switched from one zone to another to obtain a constant datatransfer rate and a substantially constant linear velocity throughoutthe zone.

When the ZCLV method is used, the following problems will arise. In theZCLV method, the rotational speed of the disk need be changed while thelight spot crosses a zone boundary. In addition, when the light spot hasmoved from one zone to another, a certain time is required until therotational speed of the disk settles (or stabilizes) at the stipulatedrotational speed for the zone to which the light spot has moved. Duringthe settling time, the interval between the sectors varies. Then, sectorsynchronization may be temporarily lost, in which case it is necessaryto re-establish the sector synchronization quickly. It is also necessaryto detect a connecting point between a land track and a groove trackquickly and accurately.

An optical disk drive apparatus for driving a conventional land/grooverecording optical disk is described next. FIG. 18 is a block diagramshowing the configuration of the conventional optical disk driveapparatus described in Japanese Unexamined Patent Publication 6-176404.Referring to FIG. 18, reference numeral 100 indicates an optical disk,101 indicates a semiconductor laser, and 102 indicates a collimator lensfor converting a laser beam from the semiconductor laser 101 into aparallel beam. Reference numeral 103 indicates a half mirror, 104indicates an objective lens for focusing the parallel beam which haspassed through the half mirror 103 onto the optical disk, and referencenumeral 105 indicates a photodetector for receiving the beam which hasbeen reflected from the optical disk 100, and has passed through theobjective lens 104 and the half mirror 103. The photodetector 105includes two light-receiving parts divided by a boundary line extendingin a direction parallel and to the track direction of the disk so as toobtain a tracking error signal. Reference numeral 106 indicates anactuator supporting the objective lens 104, and a portion 107 enclosedby a dotted line represents an optical head mounted on a head base.Reference numeral 108 indicates a differential amplifier for receivingdetection signals from the photodetector 105, and reference numeral 109indicates a polarity reversal circuit for receiving the tracking errorsignal from the differential amplifier 108, and a control signal T1 froma system controller 121 which will be hereinafter described, and forsupplying the tracking error signal to a tracking controller 110. Thepolarity of the tracking control is such that when the tracking errorsignal is supplied from the differential amplifier 108 to the trackingcontroller 110 without having its polarity reversed, the light spot ispulled into a groove track. Reference numeral 110 indicates the trackingcontroller for receiving the output signal from the polarity reversalcircuit 109 and a control signal T2 from the system controller, and forsupplying tracking control signals to a driver 120 and a traversecontroller 116. Reference numeral 111 indicates a summing amplifier forreceiving the detection signals from the photodetector 105 and forsupplying the sum signal, and reference numeral 112 indicates a waveformshaping circuit for receiving a high-frequency component of the outputsignal from the summing amplifier 111 and for supplying digital signalsto a reproduced signal processor 113 and an address reproduction circuit114 which will be hereinafter described. Reference numeral 113 indicatesthe reproduced signal processor for supplying reproduced data to anoutput terminal. Reference numeral 114 indicates the addressreproduction circuit for receiving the digital signal from the waveformshaping circuit 112 and for supplying an address signal to an addresscalculator 115 which will be hereinafter described. Reference numeral115 indicates the address calculator for receiving the address signalfrom the address reproduction circuit 114 and the control signal T1 fromthe system controller 121 and for supplying the correct address signalto the system controller 121. Reference numeral 116 indicates a traversecontroller for providing a driving current to a traverse motor 117 whichwill be hereinafter described, in response to a control signal T3 fromthe system controller 121. Reference numeral 117 indicates the traversemotor for moving the optical head 107 in the radial direction of theoptical disk 100. Reference numeral 118 indicates a recording signalprocessor for receiving recording data and supplying a recording signalto a laser diode (LD) driver 119 which will be hereinafter described.The LD driver 119 receives a control signal T4 from the systemcontroller 121 and the recording signal from the recording signalprocessor 118 and supplies a driving current to the semiconductor laser101. Reference numeral 120 indicates a driver for supplying a drivingcurrent to the actuator 106. Reference numeral 121 indicates the systemcontroller for supplying the control signals T1 through T4 to thetracking controller 110, the traverse controller 116, the addresscalculator 115, the polarity reversal circuit 109, the recording signalprocessor 118, and the LD driver 119.

The operation of the conventional optical disk drive apparatus havingthe above-mentioned configuration is described with reference to FIG.18. The laser beam emitted from the semiconductor laser 101 is made tobe parallel by the collimator lens 102, passed through the beam splitter103, and focused onto the optical disk 100 by the objective lens 104.The laser beam reflected from the optical disk 100 contains data onrecording tracks, and passed through the objective lens 104 and directedto the photodetector 105 by the beam splitter 103. The photodetector 105converts the intensity and the distribution of light in the incominglight beam to electrical signals, and supplies them to the differentialamplifier 108 and the summing amplifier 111. The differential amplifier108 applies a current-to-voltage conversion (I-V conversion) to theinput currents and supplies the potential difference between the twoinput signals, as a push-pull signal.

The polarity reversal circuit 109 determines whether a track beingaccessed is a land track or a groove track in accordance with thecontrol signal TI from the system controller, and reverses a polarityonly when the track being accessed is a land track, for example. Thetracking controller 110 supplies a tracking control signal to the driver120 according to the level of the tracking error signal. The driver 120supplies the driving current to the actuator 106 in accordance with thetracking control signal and controls the position of the objective lens104 laterally of the data recording tracks. The light spot thereby scansthe data recording tracks accurately.

On the other hand, the summing amplifier 111 applies acurrent-to-voltage conversion (I-V conversion) to output currents fromthe light-receiving parts 105, adds the input signals, and supplies theresult as the sum signal to the waveform shaping circuit 112. Thewaveform shaping circuit 112 slices the data signal and the addresssignal in analog form with a predetermined threshold value and suppliespulse trains to the reproduced signal processor 113 and the addressreproduction circuit 114, respectively. The reproduced signal processor113 demodulates the input digital data signal, applies error correction,and supplies it as reproduced data.

The address reproduction circuit 114 demodulates the input digitaladdress signal and supplies the result of the demodulation as diskposition data to the address calculator 115. The address calculator 115calculates the address of a sector being accessed, based on the addresssignal read from the optical disk 100 and the land/groove signal fromthe system controller 121 indicating whether a track being accessed is aland track or a groove track. The manner of address calculation will bedescribed later. Based on the address signal, the system controller 121determines whether the light beam is scanning a desired sector.

At the time of moving the optical head, in response to the controlsignal T3 from the system controller 121, the traverse controller 116supplies a driving current to the traverse motor 117 so as to move theoptical head 107 to a target track. At this time, the trackingcontroller 110 temporarily stops a tracking servo in response to thecontrol signal T2 from the system controller 121. During normal datareproduction, the traverse motor 117 is driven in response to thetracking error signal from the tracking controller 110 so as to move theoptical head 107 gradually in the radial direction of the disk with theprogress of data reproduction. The recording signal processor 118 addserror correction codes to the recording data which have been supplied atthe time of data recording, and supplies an encoded recording signal tothe LD driver 119. When the system controller 121 has set the mode ofthe LD driver 119 to the data recording mode by means of the controlsignal T4, the LD driver 119 modulates a driving current to be appliedto the semiconductor laser 101 in accordance with the recording signal.The intensity of a light spot of the beam emitted onto the optical disk100 is thereby changed according to the recording signal, and recordingmarks are formed.

On the other hand, during data reproduction, the mode of the LD driver119 is set to the data reproduction mode by means of the control signalT4, and the LD driver 119 controls the driving current in such a mannerthat the semiconductor laser 101 emits a laser beam of a constantintensity. The recording marks and prepits on the data recording trackscan be thereby detected.

In such a conventional optical disk drive apparatus, an identificationsignal is reproduced based on the sum signal having been processed bythe waveform shaping circuit 112. In an SS-L/G format disk as well, aconnecting point between a land track and a groove track will bereproduced, based on the sum signal having been processed by thewaveform shaping circuit 112. For this reason, in order to detect aconnecting point with a high reliability, it is necessary to set a pitpattern for an identification signal representing address data and a pitpattern for detecting a connecting point to be quite different.

Even where reproduction of data or an address is not ready because it isimmediately after a light spot has been pulled into a track, aconnecting point must be detected. Thus, a pit pattern for detecting aconnecting point should be reproducible even when the synchronizationhas not been achieved. For this purpose, it is necessary to allocatelong pits, and to provide prepits of a pit pattern of a low frequency,i.e., of long pits. In a large-capacity optical disk which aims at thesmallest possible redundancy and increase of an effective recordingdensity, allotting long pits to the pit pattern is not desirable.

A conventional land/groove recording optical disk medium and aconventional optical disk drive apparatus are configured as describedabove. Thus, when the method of inserting identification signals used inthe conventional optical disk is applied to a single spiral land/grooverecording format, it is difficult to detect a connecting point between aland track and a groove track with a high reliability.

Further, if a pit pattern permitting discrimination from theidentification signal and detection of a connecting point easily isallotted to the connecting point, long pits are necessary. An effectiverecording density is thereby reduced.

With a single spiral land/groove format, tracking offset compensationneeds to be carried out quickly and accurately. However, detection of atracking offset is difficult.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems, and its object is to provide an optical disk medium of asingle spiral land/groove format in which a connecting point between aland track and a groove track can be detected easily and correctly and atracking servo polarity can be switched accordingly, without reductionin the effective recording density, and in which tracking offsetcompensation can be made quickly and accurately. The invention also aimsat providing an optical disk drive apparatus for driving theabove-recited optical disk medium, and a tracking method for the opticaldisk medium.

It is another object of the present invention to provide an optical diskmedium with which quick re-establishment of sector synchronization afterthe passage of a zone boundary by a light spot is possible and an accessspeed is therefore improved, where a single spiral land/groove format isapplied to the ZCLV method in which the rotational speed of the disk andthe number of sectors vary depending the zone, or the ZCAV method inwhich the number of sectors or a data frequency vary depending on thezone. The invention also aims at providing an optical disk driveapparatus for driving the above-recited optical disk medium and atracking method for the disk.

According to one aspect of the invention, there is provided an opticaldisk medium using both grooves formed annularly on the disk and landsbetween the grooves for data recording parts, and recording data signalsby a localized optical constant variation or a change in a physicalshape due to application of a laser beam, the recording tracks ofgrooves each corresponding to one revolution of the disk medium, and therecording tracks of lands each corresponding to one revolution of thedisk medium being connected alternately to each other so as to form acontinuous recording spiral; wherein

said each of the recording tracks comprises an integer number ofrecording sectors of equal lengths,

an identification signal area containing an identification signalrepresenting address data or the like is provided at a leading end ofeach of the recording sectors, and positioned to align in the radialdirection with an identification signal area of an adjacent recordingsector,

the identification signal area in each of the recording sectors of thegrooves contains the identification signal, a first part of theidentification signal area is shifted by a predetermined distance in oneradial direction from a center of the groove, and a second part of theidentification signal area is shifted by the same distance in the otherradial direction from the center of the groove, and

the identification signal area in each of the recording sectors of thelands does not contain the identification signal.

With the above arrangement, in an optical disk of a single spiralland/groove recording, the arrangement of identification signals isutilized to detect a tracking polarity and a land/groove trackconnecting point reliably. As a result, stable tracking can beperformed, and a single spiral land/groove recording format can berealized in an optical disk of the sectorized configuration.

Moreover, by inserting tracking polarity information into anidentification signal, a land/groove track connecting point can bedetected reliably and information required for stable tracking can beprovided to an optical disk drive apparatus. This enables stabletracking, and a single spiral land/groove recording format can berealized for an optical disk of the sectorized configuration.

At the same time, erroneous recognition of tracking information causedby a defect, a flaw, or dust on the medium can be eliminated, andreliability of the tracking and the operations of the optical disk driveapparatus can be improved.

Further, because accurate tracking is enabled by compensating a trackingservo offset easily, reliability of data can be improved.

Further, with this optical disk, the grooves and identification signalscan be formed easily using a single laser beam at the time offabricating the master disk in mastering process of a single spiralland/groove recording format, the cost of fabrication of the disk can bereduced.

As a result, recording and reproduction can be performed throughout anentire disk continuously without seeking between a land track and agroove track, so that it is possible to achieve continuous reproductionof moving pictures for twice as long a time as in a prior art. Further,it is not necessary to provide a buffer memory for storing data to avoidinterruption of reproduction during seeking between a land track and agroove track, the cost for the apparatus for recording and reproducingdata on the optical disk medium can be reduced.

For the reasons set forth above, a single spiral land/groove recordingwhich is suitable for a video file and a data file can be realizedeasily.

It may be so arranged that the distance by which the first part or thesecond part of the identification signal area in each of the recordingsectors of the grooves in the radial direction from the center of thegroove is substantially half a recording track width.

With the above arrangement, the grooves and identification signals canbe formed easily using a single laser beam at the time of fabricatingthe master disk in the mastering process of a single spiral land/grooverecording format, the cost of fabrication of the disk can be reduced.

Further, because accurate tracking is enabled by compensating a trackingservo offset easily, reliability of data can be improved.

It may be so arranged that the first part and the second part of theidentification signal area in said each of recording sectors of thegrooves each further contains tracking polarity information for therecording sector to which the first part or the second part of theidentification signal area belongs.

With the above arrangement, in an optical disk of a single spiralland/groove recording, tracking polarity information and address dataare recorded multiple times, so that an error rate in reading addressdata in an identification signal can be reduced and reliability ofreading tracking polarity information can be improved.

According to another aspect of the invention, there is provided anoptical disk drive apparatus comprising:

an optical head having at least a push-pull tracking sensor;

a differential signal detector for generating a differential signalbased on signals from the tracking sensor;

a differential signal waveform shaping circuit for generating binarizeddifferential signals from the differential signal; and

a reproduced differential signal processor for producing anidentification signal gating signal corresponding to the identificationsignal area, from the binarized differential signals;

wherein when data is recorded on and reproduced from the optical diskmedium,

timing of a recording sector identification signal is detected accordingto the waveform of the binarized differential signal, and sectorsynchronization is ensured based on the timing.

With the above arrangement, sector synchronization is detected quickly,accurately, and easily for a single spiral land/groove recording disk.For this reason, a connecting point between a land track and a groovetrack can be detected reliably and easily.

In the ZCLV method in which the rotational speed of the disk and thenumber of sectors vary from one zone to another, sector synchronizationafter the passage of a zone boundary by a light spot can bere-established quickly. Thus, the effect of the invention is remarkable,and an access speed can be increased. In the ZCAV method as well, inwhich the number of sectors and a data frequency vary from one zone toanother, sector synchronization after the passage of a zone boundary bya light spot can be re-established quickly. Thus, the effect of theinvention is remarkable, and an access speed can be increased.

According to another aspect of the invention, there is provided anoptical disk drive apparatus comprising:

an optical head having at least a push-pull tracking sensor;

a differential signal detector for generating a differential signalbased on signals from the tracking sensor;

a differential signal waveform shaping circuit for generating binarizeddifferential signals from the differential signal;

a reproduced differential signal processor for determining whether therecording sector is in a land or a groove based on the binarizeddifferential signals and for supplying a polarity detection signal; and

a polarity controller for setting a tracking servo polarity by using thepolarity detection signal;

wherein when data is recorded on or reproduced from the optical diskmedium, determination is made, during reproduction of the first part andthe second part of an identification signal area in said each of therecording sectors, as to whether the recording sector is a land sectoror a groove sector according to the radial shift directions representedby the binarized differential signals, and the order of the shiftdirections; and

a tracking servo polarity for tracking a data recording part of therecording sector is set, based on the result of the determination.

With the above arrangement, in an optical disk of a single spiralland/groove recording, the arrangement of identification signals isutilized to detect a tracking polarity and a land/groove trackconnecting point reliably. A single spiral land/groove recording formatcan therefore be realized in an optical disk of the sectorizedconfiguration.

As a result, recording and reproduction can be performed throughout anentire disk continuously without seeking between a land track and agroove track, so that it is possible to achieve continuous reproductionof moving pictures for twice as long a time as in a prior art. Further,it is not necessary to provide a buffer memory for storing data to avoidinterruption of reproduction during seeking between a land track and agroove track, the cost for the apparatus for recording and reproducingdata on the optical disk medium can be reduced.

For the reasons set forth above, a single spiral land/groove recordingwhich is suitable for a video file and a data file can be realizedeasily.

According to another aspect of the invention, there is provided anoptical disk drive apparatus comprising:

an optical head having at least a push-pull tracking sensor;

a sum signal detector for generating a sum signal based on signals fromthe tracking sensor;

a sum signal waveform shaping circuit for generating binarized sumsignals from the sum signal;

a reproduced signal processor for reproducing data from the binarizedsum signals; and

a polarity controller for setting a tracking servo polarity;

a sum signal waveform shaping circuit for generating binarized sumsignals from the sum signal;

a reproduced signal processor for reproducing data from the binarizedsum signals; and

a polarity controller for setting a tracking servo polarity;

wherein when data is recorded on and reproduced from the optical diskmedium,

determination is made as to whether each of the recording sectors is aland sector or a groove sector according to the tracking polarityinformation contained in the reproduced data from the identificationsignal areas of the recording sectors, and a tracking servo polarity fortracking a data recording part of the recording sector is set accordingto the polarity information.

With the above arrangement, in an optical disk of a single spiralland/groove recording, the information of identification signals isutilized to detect a tracking polarity and a land/groove trackconnecting point reliably. A single spiral land/groove recording formatcan therefore be realized in an optical disk of the sectorizedconfiguration.

As a result, recording and reproduction can be performed throughout anentire disk continuously without seeking between a land track and agroove track, so that it is possible to achieve continuous reproductionof moving pictures for twice as long a time as in a prior art. Further,it is not necessary to provide a buffer memory for storing data to avoidinterruption of reproduction during seeking between a land track and agroove track, the cost for the apparatus for recording and reproducingdata on the optical disk medium can be reduced.

For the reasons set forth above, a single spiral land/groove recordingwhich is suitable for a video file and a data file can be realizedeasily.

According to another aspect of the invention, there is provided anoptical disk drive apparatus comprising:

an optical head having at least a push-pull tracking sensor;

a sum signal detector for generating a sum signal based on signals fromthe tracking sensor;

a sum signal waveform shaping circuit for generating binarized sumsignals from the sum signal;

a differential waveform shaping circuit for generating binarized signalsfrom the differential signal;

a reproduced differential signal processor for determining whether therecording sector is in a groove or a land, based on the binarizeddifferential signals, and for supplying a polarity detection signal; and

a polarity controller for setting a tracking servo polarity by using thepolarity detection signal;

wherein

when data is recorded on and reproduced from the optical disk medium,

a connecting point between a groove track and a land track is detectedbased on the waveform of the binarized differential signal, and atracking servo polarity for tracking a data recording part in therecording sector is determined,

determination is made as to whether the sector is a groove recordingsector or a land recording sector in accordance with the trackingpolarity information contained in the reproduced data from theidentification signal area of each of the recording sectors, and

a tracking servo polarity for a data recording part of the recordingsector is set in accordance with both the tracking servo polaritydetermined and the tracking polarity information reproduced.

With the above arrangement, detection of the shift direction of anidentification signal and detection of land/groove track polarityinformation in the identification signal are both used in a singlespiral land/groove recording optical disk, a land/groove trackconnecting point can be detected with a higher reliability, duringtracking and after passage of a zone boundary, and stable tracking canbe achieved.

Thus, in addition to the effects obtained by the arrangement recitedearlier, an even higher reliability in tracking and operation of theapparatus can be obtained.

According to another aspect of the invention, there is provided anoptical disk tracking method, wherein

after tracking has been applied to either of a groove or a land,

in case that a differential signal generated on the basis of signalsfrom the tracking sensor or a differential band-limited signal obtainedby filtering the differential signal through a band-pass filter is morethan a first specified value for a first predetermined period and thenis less than a second specified value for a second predetermined period,a tracking servo polarity is set such that a predetermined one of thegroove or the land is tracked,

in case that a differential signal generated on the basis of signalsfrom the tracking sensor or a differential band-limited signal obtainedby filtering the differential signal through a band-pass filter is lessthan a second specified value for a first predetermined period and thenis more than a first specified value for a second predetermined period,a tracking servo polarity is set such that the other of the groove orthe land is tracked.

With the above arrangement, in an optical disk of a single spiralland/groove recording, the arrangement of identification signals isutilized to detect a tracking polarity and a land/groove trackconnecting point reliably. As a result, stable tracking can beperformed, and a single spiral land/groove recording format can berealized in an optical disk of the sectorized configuration.

At the same time, erroneous recognition of tracking information causedby a defect, a flaw, or dust on the medium can be eliminated, andreliability of the tracking and the operations of the optical disk driveapparatus can be improved.

As a result, recording and reproduction can be performed throughout anentire disk continuously without seeking between a land track and agroove track, so that it is possible to achieve continuous reproductionof moving pictures for twice as long a time as in a prior art. Further,it is not necessary to provide a buffer memory for storing data to avoidinterruption of reproduction during seeking between a land track and agroove track, the cost for the apparatus for recording and reproducingdata on the optical disk medium can be reduced.

For the reasons set forth above, a single spiral land/groove recordingwhich is suitable for a video file and a data file can be realizedeasily.

According to another aspect of the invention, there is provided anoptical disk tracking method, wherein

a tracking error signal is sampled and held immediately before a lightspot scans the identification signal area of the recording sector,tracking control is stopped while the light spot is scanning theidentification signal area, and determination is made as to whether thesector is a groove recording sector or a land recording sector based onat least the tracking polarity information contained in the reproduceddata from the identification signal area, and

a tracking servo polarity for tracking the data recording part in therecording sector is set according to the result of the determination,and tracking control is resumed at the data recording part.

With the above arrangement, in an optical disk of a single spiralland/groove recording, the information of identification signals isutilized to detect a tracking polarity and a land/groove trackconnecting point reliably. As a result, stable tracking can beperformed, and a single spiral land/groove recording format can berealized in an optical disk of the sectorized configuration.

As a result, recording and reproduction can be performed throughout anentire disk continuously without seeking between a land track and agroove track, so that it is possible to achieve continuous reproductionof moving pictures for twice as long a time as in a prior art. Further,it is not necessary to provide a buffer memory for storing data to avoidinterruption of reproduction during seeking between a land track and agroove track, the cost for the apparatus for recording and reproducingdata on the optical disk medium can be reduced.

For the reasons set forth above, a single spiral land/groove recordingwhich is suitable for a video file and a data file can be realizedeasily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically showing a track layout of an opticaldisk medium according to the first embodiment of the present invention;

FIG. 2 is a drawing schematically showing the arrangement ofidentification signals within data recording sectors and their addresseson an optical disk medium according to the first embodiment of thepresent invention;

FIG. 3 is a drawing schematically showing the arrangement ofidentification signals within data recording sectors around a boundarybetween a land and a groove and their addresses on an optical diskmedium according to the first embodiment of the present invention;

FIG. 4 is a block diagram showing the configuration of an optical diskdrive apparatus according to the second embodiment of the presentinvention;

FIG. 5A to FIG. 5E are timing charts for explaining a method ofidentifying a tracking polarity of a data recording sector according tothe second embodiment of the present invention;

FIG. 6 is a circuit block diagram showing a reproduced differentialsignal processor of the optical disk drive apparatus according to thesecond embodiment of the present invention;

FIG. 7A to FIG. 7I are detailed timing charts for explaining a method ofidentifying a tracking polarity of a data recording sector according tothe second embodiment of the present invention;

FIG. 8A is a circuit block diagram of a polarity controller;

FIG. 8B is a table showing the function of the polarity controller ofthe optical drive apparatus according to the second embodiment of thepresent invention;

FIG. 9 is a circuit block diagram showing a reproduced differentialsignal processor of an optical disk drive apparatus according to thethird embodiment of the present invention;

FIG. 10 is a circuit block diagram showing a reproduced differentialsignal processor of an optical disk drive apparatus according to thefourth embodiment of the present invention;

FIG. 11A to FIG. 11K are detailed timing charts for explaining a methodof identifying a tracking polarity of a recording sector according tothe fourth embodiment of the present invention;

FIG. 12A, FIG. 12B, and FIG. 12E to FIG. 12K are detailed timing chartsfor explaining a method of identifying a tracking polarity of arecording sector according to the fifth embodiment of the presentinvention;

FIG. 13 is a drawing showing an example of conventional land/grooverecording optical disk;

FIG. 14 is a drawing showing an example of conventional optical diskhaving a single spiral land/groove recording format;

FIG. 15 is a drawing showing an example of land/groove connecting pointon a conventional single spiral land/groove recording optical disk;

FIG. 16A and FIG. 16B are diagrams showing another example of connectingpoints on conventional single spiral land/groove recording optical disk;

FIG. 17A to FIG. 17C are diagrams showing layout of identificationsignals in accordance with a conventional land/groove recording method;and

FIG. 18 is a block diagram showing the configuration of a conventionaloptical disk drive apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of this invention will be described with reference to thedrawings.

First Embodiment

This embodiment relates to a single spiral land/groove (SS-L/G) formatoptical disk medium. Description of this embodiment will be made on theassumption that the optical disk medium is divided into a plurality ofannular zones by circular boundaries.

FIG. 1 shows a track layout of an optical disk medium according to thefirst embodiment of the present invention, and shows the arrangement oftracks and recording sectors within one zone, and a configuration of therecording sector. As shown in FIG. 1, a track (groove track) G of agroove (depressed portion), and a track (land track) L of a land(projected portion) are connected at connecting points CP alternately atevery revolution to form a recording spiral (a recording track in aspiral form). It is assumed here that the width of a groove G and thewidth of a land L are identical. The width of a groove or a land isequal to a track pitch and is half a groove interval.

A recording track corresponding to one revolution of the disk iscomposed of an integer number of recording sectors. As an example it isshown to be composed of 12 sectors. At the leading end of each sector, apreformatted identification area (identification signal field) IDF isadded. An optical disk in this embodiment is different from the opticaldisk according to the prior art in that a land track and a groove trackare discontinuous because of the prepits in the identification signalarea IDF. In other words, a land track and a groove track are connectedvia the prepits in the identification signal area IDF, and theidentification signal area IDF in each sector RS has (or contains)identification data for identifying the sector and also has (orcontains) information for detecting a connecting point CP between agroove track and a land track.

Each of the recording sectors which constitute a recording track has apreformatted identification signal area at its leading end and a datarecording area DRF capable of recording user data and various managementdata.

FIG. 2 schematically shows the arrangement of prepits in identificationsignal areas within recording sectors RS on an optical disk and theiraddress values according to the first embodiment of the presentinvention. m (which is an integer) represents the address of therecording sector, and M (which is also an integer) represents the numberof sectors per track. IP represents the direction toward the innerradial part of the disk, while OP represents the direction toward theouter radial part of the disk. SCN represents the direction of thescanning of the light spot. The identification signal area consists of afront part FP and a rear part RP as viewed in the scanning direction.The front part FP is shifted by half a groove width radially outwardsfrom a groove. The rear part RP is shifted by half a groove widthradially inwards from the groove.

A method of providing identification data such as a sector address inthe identification signal area is described next. The address of asector RS in a groove (which is shown as a depressed portion in FIG. 2)G is added in a front part FP of the identification signal area IDFwhich is immediately before the data recording area DRF in the sector RSin the groove G, being shifted radially outwards by half a groove widthfrom the center of the groove G. The address of a sector RS in a land(which is shown as a projecting portion in FIG. 2) L is added in a rearpart RP of the identification signal area IDF immediately before thedata recording area DRF in a groove track G adjacent and radiallyoutward of the sector RS in the land L, being shifted radially inwardsby half a groove width from the center of the groove. As a result, theaddress of a land sector is added or provided in the rear part RP of theidentification signal area IDF in a groove immediately before the datarecording area DRF of the land sector, being shifted radially outwardsby half a groove width from the center of the land L. In this way, theaddress of a land sector is added to a groove rather than to a land, andan identification signal area in a land contains no identificationsignal.

The sector identification data of the identification signal area IDFalso has or contains information on a tracking polarity for each ofgroove sectors and land sectors as well as the sector address.

This scheme is used because a tracking offset occurring during thecutting of a master original in a mastering process will be smaller ifthe addresses of both lands and grooves are cut simultaneously duringthe cutting of groove tracks. If cutting the groove sector addressesduring cutting of the groove recording track, and cutting the landsector addresses during cutting of the land recording track (tracingland track with the laser beam turned off) will result in a smallertracking offset because of the tracking offset characteristics, cuttingof the groove sector addresses and the land sector addresses may beperformed separately.

The reason why the identification signals are shifted by half a groovewidth from the center of the track is to ensure that the identificationdata of substantially the same quality can be obtained regardless ofwhether a track being scanned is a groove track or a land track as theidentification data is shared by a groove track and a land track. Whenthe width of a groove is not identical to a track pitch, the amount ofthe shift may be set to half a track pitch.

Next, description is directed to prepits in identification signal areasaround connecting points between lands and grooves, which are present atevery revolution of a disk and aligned in a radial direction of thedisk, and a method of assigning addresses to such identification signalareas. FIG. 3 schematically shows the arrangement of identificationsignal prepits within recording sectors around boundaries betweengrooves and lands on an optical disk according to the first embodimentof the present invention, and their address values. n (which is aninteger) represents the address of the recording sector, and N (which isalso an integer) represents the number of sectors per track. In anSS-L/G format optical disk, there is a connecting point GP at which agroove track G and a land track L are connected at every revolution ofthe disk and the boundaries or connecting points CP at every revolutionare arranged in a radial direction. The arrangement of theidentification signal areas in a recording sector RS immediately after aconnecting point CP is similar to that in other recording sectors(recording sectors RS which are not at a connecting point CP) in thatthe front part FP of the identification signal area IDF is shifted byhalf a groove width radially outwards from a groove G, and the rear partRP of the identification signal area IDF is shifted by half a groovepitch radially inwards from the groove G. The assignment of addressvalues is also similar to the parts other than connecting points. Thatis, the address of a groove sector is assigned to the front parts FP ofthe identification signal area IDF, which is shifted radially outwardsby half a groove width from a groove G immediately before the datarecording area DRF of the groove sector. The address of a land sector isassigned to the rear part RP of the identification signal area IDF,which is shifted radially outwards by half a groove width from a land Limmediately before the data recording area DRF of the land sector.

To detect a connecting point CP between a groove recording track G and aland recording track L, determination is made as to which radialdirection the front part FP and the rear part RP of an identificationsignal area IDF are shifted with respect to the center of a track in astate in which tracking is achieved. The address of a groove sector canbe identified as an identification signal in the front part FP which isshifted radially outwards by half a track pitch from the groove, and theaddress of a land sector can be identified as an identification signalin the rear part RP which is shifted radially outwards by half a trackpitch from the land. In either case, the part of identification signalarea which is shifted radially outwards represents the address of thesector, while the part of the identification signal area shiftedradially inwards represents the address of a sector adjacent thereto andpositioned radially inwards.

Now, description is directed to detection of a track connecting point CPduring a seek operation. At the time of passage of a zone boundary, theoccurrence cycle of a preformatted identification signal changesstepwise, and sector synchronization tends to be lost. With an SS-L/Grecording format, it is necessary to detect a land/groove switchingpoint CP accurately even in such a circumstance.

In the ZCLV method, at the time of seeking into a different zone, theidentification signal is not detected at a predetermined time intervaluntil the rotational speed of the disk has been settled to a valuespecified for the zone, and sector synchronization is thus lost. In thecase of an ordinary land/groove recording recording disk, it waspossible to pull into tracking stably whichever of a land track or agroove track the tracking may be applied. In the case of an SS-L/Grecording disk, tracking may fail if a land/groove switching point CPappears immediately after the tracking pull-in. The probability ofoccurrence of failure of the tracking pull-in is low, and recovery canbe achieved by re-trying. However, in order to improve the speed and thereliability of the access, it is desirable to achieve a correct trackingpull-in without fail.

In the method of inserting an identification signal for an SS-L/Grecording disk described in the first embodiment, the polarity can bedetermined reliably by the order of directions of shifting of theidentification signals as described above. Thus, it is possible to avoidthe failure of a tracking pull-in which tended to occur with theconventional SS-L/G recording disk.

As one of the additional functions and effects, track offsetcompensation is described. As has been used in the optical disk standardISO/IEC 9171-1, 2 “130 mm Optical Disk Cartridge Write Once forInformation Interchange”, 1990 and the like, for an optical disk whichuses a sample servo method, a method is known in which the amount oftracking offset is detected using a pair of pits formed on a recordingtrack, being shifted in opposite directions by a predetermined distancefrom the center of the track, and the correction of the tracking offsetis applied accordingly.

When a light beam passes through the midpoint of the pair of pits, theamplitudes of reproduced signals from the detection pits will beequivalent. If the light beam is deviated from the center of the trackin one direction, the amplitude of the reproduced signal from one of thetrack offset detection pits will increase, and the amplitude of thereproduced signal from the other one of the track offset detection pitswill decrease. On the basis of the reproduced signals, it is possible todetect the amount of track offset of the light beam, and applycorrection, so that the light beam is controlled to follow the center ofthe track. According to the present invention, the same principle can beapplied to a single spiral land/groove recording format optical disk.

Let us assume that a light beam has passed through the data recordingarea (field) in a particular groove recording sector and has entered theidentification signal area of the subsequent groove sector. Because thefront part FP of the identification signal area IDF is shifted radiallyoutwards by half a track pitch, a corresponding tracking error signal isproduced. Subsequently, there appears a rear part RP of theidentification signal area IDF which is shifted radially inwards by halfa track pitch, so a corresponding tracking error signal is produced. Ifthese two tracking error signals are of the same magnitude and ofopposite polarities, it means that the light beam is scanning the centerof the track. The magnitudes of the two tracking error signals aredifferent if the light beam is deviated from the midpoint of the pair ofthe identification signal areas, and the difference between them and thepolarity of the difference depend on the amount and direction ofdeviation of the light beam from the center of the midpoint. Thus, bycomparing the magnitudes of the tracking error signals detected from thefront part and the rear parts of the identification signal area whichare shifted radially outwards and inwards, a tracking servo can becontrolled in such a manner that the light beam will scan the center ofthe track.

As described above, according to the method of the present invention ofinserting identification signals for an SS-L/G recording disk, a servocharacteristic can also be improved.

As a further additional function and effect, immunity to defects on themedium is described. Compared with the method of insertingidentification signals shown in FIG. 17B, this invention uses a waveformof a differential signal which maintains a high signal level for apredetermined period and then a low signal level for a predeterminedperiod, such a waveform appearing very rarely in the other parts of thedisk including data recording areas DRF, for representing a connectingpoint CP between a land track L and a groove track G, and anidentification signal for a sector, with the result that erroneousdetection of the identification signal or the connecting point, due toconfusion with a signal level change because of a defect on the mediumor deterioration in the recording layer, hardly happens.

On the other hand, in the method shown in FIG. 17B, a variation in adifferential signal, which is similar to that in an identificationsignal, will occur only if there is a single defect and the like on thedisk. Thus, erroneous recognition of a tracking polarity or anidentification signal can occur. In terms of the immunity to a defect onthe medium as well, this invention is advantageous over the prior art.

It is also possible to use another method of discriminating thepolarity. In addition to the address of a sector, an identificationsignal in the sector contains polarity information indicating whetherthe sector being accessed is a land sector or a groove sector, orinformation indicating the position relative to the connecting point.When tracking is achieved correctly, identification data can be readreliably, and the polarity can therefore be set according to this data.

By using the method of discriminating the polarity by means of thedirections of the shifting and their order, together with the polarityinformation in the identification signal, more accurate and reliabletracking polarity setting can be realized. Discriminating the polarityby means of only the polarity information is also possible for simpleimplementation.

As described above, the first part (FP) of an identification signal areais shifted by a predetermined distance in one radial direction, forexample, radially outwards from the center of a groove G, and the secondpart (RP) of the identification signal area is shifted by the samedistance in the other radial direction, for example, radially inwardsfrom the center of the groove G, and when data on this disk isreproduced, a tracking error signal which is obtained as a differencebetween the outputs of the light receiving parts of the tracking sensorpositioned to correspond to the radially different positions on the diskis binarized by two comparators having different threshold values, andchanges in the tracking error signal are observed. In this way, thetracking polarity for each recording sector RS can be discriminated, anda connecting point CP between a land track L and a groove track G can bedetected reliably.

Second Embodiment

This embodiment relates to an apparatus for recording and reproducingdata on the optical disk medium described in the first embodiment. FIG.4 is a block diagram showing the configuration of an optical disk driveapparatus according to second embodiment of the present invention.Referring to FIG. 4, reference numeral 100 indicates an optical disk,reference numeral 101 indicates a semiconductor laser, 102 indicates acollimator lens, 103 indicates a half mirror, 104 indicates an objectivelens, 105 indicates a photodetector, 106 indicates an actuator, 107indicates an optical head, 108 indicates a differential signal detector,109 indicates a polarity reversal circuit, 110 indicates a trackingcontroller, 111 indicates a summing amplifier, 112 indicates a sumsignal waveform shaping circuit, 116 indicates a traverse controller,117 indicates a traverse motor, 118 indicates a recording signalprocessor, 119 indicates a laser diode (LD) driver, and referencenumeral 120 indicates a driver. These structural elements are basicallyidentical to those of the optical disk drive apparatus illustrated inFIG. 18. Thus, like reference numerals are assigned to these structuralelements and description thereof is omitted.

The structural elements which are different from those illustrated inFIG. 18 are described. Reference numeral 1 indicates a differentialsignal waveform shaping circuit for binarizing the tracking error signalin analog waveform from the differential signal detector 108 inaccordance with an appropriate signal level, and outputting theresultant binarized differential signals. Reference numeral 2 indicatesa reproduced differential signal processor for extracting theidentification signal from the binarized differential signal todetermine the tracking polarity, and for supplying polarity detectionsignals to the polarity controller 8, a polarity informationreproduction circuit 4, an address reproduction circuit 5, and a datareproduction circuit 6. Reference numeral 8 indicates a polaritycontroller for receiving the polarity detection signal from thereproduced differential signal processor 2 and a control signal from thesystem controller 7 and for supplying a polarity setting signal to thepolarity reversal circuit 109 and a control hold signal to the trackingcontroller 110.

Reference numeral 3 indicates the reproduced signal processor forreproducing an identification signal containing address data andpolarity information from binarized sum signals obtained by applyingwaveform processing to the sum signal. Reference numeral 4 indicates thepolarity information reproduction circuit for extracting polarityinformation indicating the tracking polarity of a sector, from theidentification signal. Reference numeral 5 indicates the addressreproduction circuit for reproducing sector address data from theidentification signal. Reference numeral 6 indicates the datareproduction circuit for reproducing user data recorded in datarecording areas on the disk. The reproduced polarity information and theaddress data are supplied to the system controller 7 and used forcontrol over the sample-hold state in the tracking control, and thetracking polarity.

Reference numeral 7 indicates the system controller for receiving dataon the identification signal from the reproduced differential signalprocessor 2, the polarity information reproduction circuit 4, and theaddress reproduction circuit 5, and for supplying control signals to thepolarity controller 8, the traverse controller 116, the LD driver, andthe recording signal processor 118.

The operation before and after a connecting point between a groove trackand a land track of an optical disk is described.

FIG. 5A to FIG. 5E show the procedure and the method for applyingtracking to an SS-L/G format disk illustrated in FIG. 2 and FIG. 3. FIG.5A shows the arrangement of grooves G and preformatted identificationsignals ID. The front part FP of an identification signal area IDF in agroove G is shifted by substantially half a track pitch radiallyoutwards with respect to the center of a groove G, and the rear part RPis shifted by substantially half a track pitch radially inwards withrespect to the center of the groove G. Thus, for the light spot scanningalong a spiral, the order of the directions of the shifting of theidentification signals ID is reversed at a connecting point CP. That is,when the light spot is scanning a groove track G for example, thedirection of the shifting of the identification signals ID is radiallyoutwards first, and then radially inwards. When the light spot crosses aconnecting point CP, and begins to scan a land track L, the direction ofthe shifting of the identification signals ID is radially inwards first,and then radially outwards, as will be seen from FIG. 5A.

FIG. 5A through FIG. 5E show the operations of a tracking system and anidentification signal detection system when a light spot is passingthrough preformatted identification signal area of a land/grooveswitching sector and other, ordinary sectors, and a land/grooveswitching mechanism. FIG. 5A schematically illustrates the arrangementof the identification signal ID and a light beam spot BS on a disksurface. FIG. 5B shows a tracking error signal TES, FIG. 5C shows thestate SSV of a tracking servo system control operation, FIG. 5D shows anidentification signal detection window signal WIN, and FIG. 5E showsreadout data RDT of a preformatted identification signal containingtracking polarity information. POL(G) represents a L/G polarityinformation indicating a groove, and POL(L) represents a L/G polarityinformation indicating a land.

For describing the behavior of a tracking error signal TES when a lightbeam spot BS passes through an identification signal area IDF, a lightbeam spot BS which is tracking a groove track, for example, isconsidered. FIG. 5B shows the tracking error signal TES or differentialsignal of a push-pull tracking sensor obtained when the light beam istracing a data recording track.

While a light spot is passing through the identification signal area IDFof an ordinary groove sector, the front part FP of the identificationsignal area IDF is shifted radially outwards, and a tracking errorsignal TES indicating that the light spot BS is shifted radially inwardsby substantially half a track pitch from the center of a groove G, i.e.,indicating the maximum shift is obtained. As the rear part RP of theidentification signal area IDF is shifted radially inwards, a trackingerror signal TES indicating that the light spot BS is shifted radiallyoutwards by substantially half a track pitch from the center of thegroove G, i.e., indicating the maximum shift in the opposite directionis obtained.

In this way, from the fact that the tracking error signal TES duringreproduction of data in an identification signal area IDF indicatesthat, in the front part FP of the identification signal area IDF, thetracking is deviated radially inwards, and that in the rear part RP, thetracking is deviated radially outwards, it can be determined that thedata recording area DRF in the recording sector RS after thisidentification signal area IDF is in a groove track G. Such a behaviorof a tracking error signal TES in the identification signal area IDF iscommonly seen in any groove track sector.

Next, description is directed to a change in a tracking error signal TESat a boundary CP for transition from a groove track G to a land track L.In an identification signal area IDF of a land sector, the front part FPis shifted radially inwards and the rear part RP is shifted radiallyoutwards. Thus, a tracking error signal TES indicating that in the frontpart FP of the identification signal area IDF, a light spot BS isshifted by substantially half a track pitch radially outwards from thecenter of a groove G, i.e., half a track pitch radially inwards from thecenter of a land L, will be produced, and a tracking signal indicatingthat in the rear part of the identification signal area IDF, a lightspot BS is shifted by substantially half a track pitch radially inwardsfrom the center of a groove G will be produced.

As described above, because a tracking error signal TES during thereproduction of data in an identification signal area IDF indicates thatin the front part FP of the identification signal area IDF, the trackingis shifted radially outwards and that in the rear part RP the trackingis shifted radially inwards, it can be determined that the datarecording area DRF of the recording sector RS after this identificationsignal area IDF is in a land track L. Such a behavior of the trackingerror signal TES in an identification signal area IDF is commonly seenin any land track sector.

In an identification signal area IDF at the leading end of each tracksector, the polarity change of a tracking error signal (i.e., whetherthe tracking error signal TES indicates radially inward shift first andthen radially outward shift, or radially outward shift first and thenradially inward shift) is reversed, with respect to the leading end ofeach of the track sectors which have been traced up to then. Thetracking error signal TES which is obtained in this manner while a lightspot BS is passing through an identification signal area IDF isbinarized by the converters having threshold values Lth and Rthindicated by chain lines as illustrated in FIG. 5B so as to obtainbinarized signals. According to the polarities of the binarized signalscorresponding to the front part FP and the rear part RP of theidentification signal area IDF, it can be determined whether the sectorbeing traced is in a land track L or a groove track G.

Generally, a tracking servo system is designed to have such a responsecharacteristic that the system will not respond to the short length ofan identification signal area IDF. Even if a tracking error signal TESis produced during the tracing of the identification signal area IDF,the light beam BS generally keeps on tracing the side edge of thepreformatted pits (or whatever position it has assumed upon entry intothe identification signal area). Alternatively, as a practical method,in order to shut off the tracking servo system from undesirabledisturbance, the tracking error signal may be sampled immediately beforethe light spot scans the identification signal area IDF, and held, andthe light spot is made to pass the identification signal area IDF bymeans of inertia with no tracking control exercised. FIG. 5C shows suchan operation.

Identification signal data such as sector addresses are read out byapplying sector synchronization protection by means of an identificationsignal detection window signal IDG as shown in FIG. 5D, to theperiodically appearing identification signals, and by implementingre-synchronization for each sector. By inserting data (POL) on aland/groove tracking polarity into an identification signal, land/grooveswitching can be performed reliably. In addition, by utilizing anidentification signal detection window signal IDG for the sectorsynchronization protection to gate a tracking error signal TES anddiscriminating the error polarity as described above, a land/grooveswitching point CP which occurs once a revolution of the disk can bedetected easily, and reliability of tracking polarity switching andtracking polarity setting in SS-L/G recording can be improved.

Now, description is directed to the signal processing procedure forimplementing the method of detecting a land/groove track connectingpoint CP described above, by means of the circuit blocks in an opticaldisk drive apparatus relating to tracking and identification signaldetection.

FIG. 6 shows block configuration of the differential signal detector108, the differential signal waveform shaping circuit 1, and thereproduced differential signal processor 2. FIG. 7A to FIG. 7I showchanges of signals while a recording track is being tracked. FIG. 7Ashows the arrangement of the identification signals on the disk surface.A differential amplifier constituting the differential signal detector108 determines a difference between two output signals from thetwo-split photodetector 105, and outputs the difference as adifferential signal DFS to be used for the push-pull tracking servosystem.

The differential signal DFS is binarized by the differential signalwaveform shaping circuit 1. In order to detect that prepits in anidentification signal area IDF are shifted by half a track pitchrightwards and leftwards with respect to the light beam scanningdirection, two comparators 1 a and 1 b having a threshold value Lth anda threshold value Rth are provided, and a binarized L0 signal indicatinga leftward (radially inward) shift of the light beam tracking, withrespect to the tracing direction, and a binarized R0 signal indicating arightward (radially outward) shift, as shown in FIG. 7C and FIG. 7D aregenerated. If the level of the differential signal DFS is not less thanLth, the L0 signal is made High. If the level of the differential signalDFS is not more than Lth, the L0 signal is made Low. If the level of thedifferential signal DFS is not more than Rth, the R0 signal is madeHigh. If the level of the differential signal DFS is not less than theRth level, the R0 signal is made Low. FIG. 7C and FIG. 7D show the L0and R0 signals, respectively. The values of Lth and Rth are set, forexample, to the level of the differential signal DFS produced when thetracking deviation is equivalent to a quarter of a track pitch. If theset values are too small, erroneous detection of a land/groove trackconnecting point CP may occur when a tracking deviates due to thedisturbance. If the set values are too great, shift of an identificationsignal could be overlooked due to a variation in the reflective indexcaused by dust or the like on the disk. For this reason, the thresholdvalues, for example, may be set to an appropriate values between them.It may be at the center of the amplitude of an identification signal, asshown in FIG. 7B.

The binarized differential signals are digitized by the reproducedsignal processor 2, which outputs a polarity discrimination signal (GP,LP) indicating whether the sector being traced is a land sector or agroove sector. The reproduced signal processor 2 also generates adetection gating signal IDG for estimating an occurrence interval of anidentification signal. As shown in FIG. 6, the reproduced differentialsignal processor 2 comprises a delay circuit 2 a, a determinationcircuit 2 b, and a detection gating circuit 2 c.

Because an identification signal is represented by a prepit sequenceformed of intermittent grooves modulated by the data, the two binarizeddifferential signals L0 and R0 are also modulated by the data signal.The delay circuit 2 a monitors each of the two input binarizeddifferential signals L0 and R0, and determines whether the pulse trainwhich is obtained by reproducing the prepit sequence continues for atleast a predetermined period of t1. Then, as shown in FIG. 7E and FIG.7F, when the pulse train has continued for at least the predeterminedperiod ti, the delay circuit 2 a supplies an L detection signal L1 andan R detection signal R1. The signals L1 and R1 have a pulse width of t3so that these signals are High for at least until the light spot haspassed through the identification signal area. The pulse width t1 shouldbe set to be as long as possible so as to be discriminated from noisessuch as the one caused by a defect on the medium and the like. The pulsewidth t1, however, should be shorter than the length of anidentification signal area, allowing for a certain margin taking accountof the variation in the linear velocity of the optical disk.

With regard to an identification signal for a groove sector, a pulsetrain of the L0 signal continues for at least the period t1 first, andthen a pulse train of the R0 signal continues for at least the periodt1. Let us assume now that the front part FP and the rear part RP of anidentification signal area IDF are recognized correctly. Then, when theR1 signal rises from Low to High, the L1 signal is High. When the L1signal rises from Low to High, the R1 signal is still Low.

The L1 signal is latched at the rising edge of the R1 signal to generatea GP signal as shown in FIG. 7G, and the R1 signal is latched at therising edge of the L1 signal to generate an LP signal as shown in FIG.7H. With regard to an identification signal for a groove sector, whenboth of the front part FP and the rear part RP of an identificationsignal area IDF are recognized correctly, the GP signal is High, whilethe LP signal is Low.

On the other hand, with regard to an identification signal for a landsector, a pulse train of the R0 signal continues for at least the periodt1 first, and then a pulse train of the L0 signal continues for at leastthe period t1. Thus, if the front part FP and the rear part RP of anidentification signal area IDF are recognized correctly, when the L1signal rises from Low to High, the R1 signal is already High, and whenthe R1 signal rises from Low to High, the L1 signal is still Low.Therefore, with regard to an identification signal for a land sector,when both of the front part FP and the rear part RP of an identificationsignal area IDF are recognized, the LP signal is High, while the GPsignal is Low. Thus, LP signal represents a land polarity detectionsignal LP which is High when the sector being traced is a land sector,while the GP signal represents a groove polarity detection signal whichis High when the sector being traced is a groove sector. Either of thesetracking polarity detection signals is High depending on anidentification signal for each data recording sector.

Upon expiration of a period corresponding to the data recording part DRFof the sector RS after either of the LP signal and the GP signal rises,an identification signal for a subsequent sector is reproduced. The twotracking polarity detection signals LP and GP are reset to Low,immediately before the identification signal for the subsequent sector.This reset process is carried out at a rising edge of an identificationarea detection gating signal denoted by IDG in FIG. 7I. The IDG signalis for estimating the time after detection of the identification signalin one sector to an identification signal in a subsequent sector. It isreset to Low when the polarity detection signal GP or LP goes High, andgoes High immediately before the occurrence of the identification signalin the next sector, i.e., upon expiration of time During trackingperformed with the normal sector synchronization being applied and withidentification signals being read, an identification signal appearswhile the IDG signal is High, so that the IDG signal has a function ofan estimation gating signal for removing noises in the differentialsignal generated while the IDG signal is Low and for extractingidentification signals.

In this way, during tracking, on the basis of the differential signalalone, the presence of the identification signals and the direction ofshift of the identification signals can be detected, and according tothe shift direction and the order of the directions of the shifting ofthe identification signals, it can be detected whether the sector beingtraced is a land sector or a groove sector. According to this method, itis possible to determine for each sector whether a connecting point CPbetween a land track and a groove track is present. Thus, reliabledetection of the connecting point can be achieved.

When the synchronization of an identification signal, i.e., the sectorsynchronization is lost, the identification area detection gating signalIDG is High, so that if identification signals are contained in thebinarized signals, timing of the identification signal can be detected,and sector synchronization can be established quickly, as is clear fromthe above description.

Because an identification signal is detected from a differential signal,a signal having a high level does not appear in the differential signalafter a tracking pull-in, except at the part of the identificationsignals, regardless of whether or not data is recorded in data recordingareas. This will be understood from the fact that a tracking errorsignal is scarcely produced while a tracking servo is applied normally.Thus, there is clearly an advantage that an identification signal iseasily detected.

The operation of the polarity controller will be described next. FIG. 8Ashows the configuration of the polarity controller 8. The polaritycontroller 8 has a function of receiving the polarity detection signalsGP and LP, supplying a polarity setting signal LGSET specifying atracking polarity to the polarity reversal circuit 109, and supplying acontrol hold signal HOLD directing the continuation or holding of thecontrol to the tracking controller 110. In connection with the trackingON/OFF operation included in the control sequence for the apparatus, thepolarity controller 8 receives a TS control signal TSC as well from thesystem controller 7. By the combination of these signals, the trackingcontroller 110 determines a tracking polarity and the control operation.

FIG. 8A shows a circuit block of the polarity controller 8. FIG. 8Bshows the states of the two polarity detection signals GP and LP and theidentification area detection gating signal IDG, and an example oftracking polarity setting for each state. When an identification signalis detected correctly and one of the polarity detection signals GP andLP is High, the tracking polarity may be set to that of the polaritydetection signals which is High. That is, if the polarity detectionsignal GP is High, the tracking polarity may be set to be one for agroove. If the polarity detection signal LP is High, the trackingpolarity may be set to be one for a land. It is convenient from aviewpoint of apparatus control if a default state is set, and in theexample under consideration, the default state is set to be a groovepolarity. When the tracking polarity setting signal LGSET is High, aland is tracked. When the tracking polarity setting signal LGSET is Low,a groove is tracked. However, when a light spot is in an identificationsignal area, the HOLD signal is transmitted to the tracking controller110 so as to halt the tracking control temporarily.

FIG. 5C shows the three states of this tracking control including landtracking, groove tracking, and a tracking control halt by the threelevels of a single signal.

Third Embodiment

Another embodiment of the present invention will be describedspecifically with reference to the drawings.

FIG. 9 is a block diagram showing another example of configuration ofthe reproduced differential signal processor 2. The signals while arecording track is being tracked are identical to those illustrated inFIG. 7A to FIG. 7I. The signals of the outputs from the two-splitphotodetector 105 to the binarized differential signals are identical tothose shown in FIG. 6 and FIG. 7A to FIG. 7I. In this embodiment, asshown in FIG. 9, the reproduced differential signal processor 2comprises two blocks, i.e., a counter circuit 2 d and a determinationcircuit 2 e.

Because an identification signal is represented by a sequence ofprepits, formed of intermittent grooves due to modulation by data, thetwo binarized differential signals L0 and R0 from the differentialsignal waveform shaping circuit 1 also have the waveform of the prepitsequence modulated by the data signal. The counter circuit 2 d monitorseach of the two input binarized differential signals L0 and R0, anddetermines whether at least a predetermined number of pulses occurwithin a predetermined period t2 (t2>t1). When the predetermined numberof pulses have occurred, the L detection signal L1 and the R detectionsignal R1 are produced. The L1 and R1 signals respectively have a pulsewidth of t3 so that these signals are High at least until the completionof the tracing of the identification signal area IDF. As was describedin connection with the second embodiment, the pulse width t1 is set tobe as long as possible so as to be discriminated from noise such as thatcaused by a defect on the medium and the like. The pulse width t1,however, should be shorter than the length of an identification signalarea, allowing for a certain margin taking account of the variation inthe linear velocity of the optical disk.

Because the identification signal area contains a stipulated number ofpreformatted data specified in the format, at least a predeterminednumber of pulses are contained in each of the front part FP and the rearpart RP of the identification signal area IDF. An identification signalcan be detected on condition that at least a predetermined number ofpulses are input within a specified period.

In the reproduced differential signal processor circuit 2 illustrated inFIG. 9, the L0 signal is supplied to the up input U of a first up-downcounter 2da, and clock pulses CLK for counting the determination periodt2 are input to the down input D, and a clear signal CLR for removingnoise pulses is supplied. Specifically, clock signals of a low frequencymay be used as the clock pulses CLK for counting the determinationperiod. In the up-down counter 2da, when an identification signal areais traced, the pulses of the L0 signal are counted to a stipulatednumber and the L1 signal goes High. The L1 signal continues to be Highfor the period t3. After the elapse of the period t3, the L1 signal isreset by a t3 timer 2db. The t3 timer 2db clears (resets) the up-downcounter 2da, the period t3 after the L1 signal goes High.

The R0 signal is supplied to the up input U of a second up-down counter2dc, and clock pulses CLK for counting the determination period t2 isinput to the down input D, and a clear signal CLR for removing noisepulses is supplied. This up-down counter 2dc is cleared by a t3 timer2dd, and the operations of the up-down counter 2dc and the t3 timer 2ddare identical to those of the up-down counter 2da to which L0 is inputand the t3 timer 2db. But R1 signal rather than L1 signal is produced.

In the determination circuit 2 e, determination is made based on the L1and R1 signals to produce the polarity detection signals GP and LP, inthe same way as in the second embodiment. The recognition anddetermination of an identification signal for a groove sector or a landsector can be performed, as in the first embodiment.

Fourth Embodiment

Another embodiment of the present invention will be describedspecifically with reference to the drawings.

FIG. 10 shows another block configuration of the differential signaldetector 108, the differential signal waveform shaping circuit 1, andthe reproduced differential signal processor 2. FIG. 11A to FIG. 11Kshow the signals while a recording track is being tracked. FIG. 11Ashows the arrangement of the identification signals on the disk surface.The signals at the outputs of the two-split photodetector 105 to thebinarized differential signals are identical to those shown in FIG. 6and FIG. 7A to FIG. 7I. As shown in FIG. 10, the reproduced differentialsignal processor 2 comprises four blocks, namely a correction circuit 2f, a delay circuit 2 g, a determination circuit 2 h, and a detectiongating circuit 2 i.

Because an identification signal is represented by a sequence ofprepits, formed of intermittent grooves due to modulation by data, thetwo binarized differential signals L0 and R0 from the differentialsignal waveform shaping circuit 1 also have the waveform of the prepitsequence modulated by the data signal. The correction circuit 2 fcorrects the pit sequence waveform using a re-triggerable mono-stablemultivibrator, for example, so that each of the front part FP and therear part RP of the identification signal forms a single, continuouspulse, to thereby enable detection of the presence or absence of thefront part FP and the rear part RP of the identification signal areaIDF, from the two input binarized differential signals. The L0 signal iscorrected to generate a binarized corrected differential signal L2, andthe R0 signal is corrected to generate a binarized correcteddifferential signal R2.

The delay circuit 2 g monitors each of the two input binarizeddifferential signals L2 and R2, and determines whether a pulse sequenceobtained by reproducing the prepit sequence continues for at least apredetermined period t1. If the pulse sequence has continued for atleast the predetermined period t1, an L detection signal L3 and an Rdetection signal R3 are produced. The L3 and R3 signals respectivelyhave a pulse width of t3 so that these signals are High at least untilthe completion of the tracing of the identification signal area.

The recognition and determination of an identification signal for agroove sector or a land sector can be performed, as in the secondembodiment.

Fifth Embodiment

Another embodiment of the present invention will be describedspecifically with reference to the drawings.

FIG. 12A, FIG. 12B and FIG. 12E to FIG. 12K show an example where theprocess at the differential signal waveform shaping circuit 1, describedin connection with the third embodiment, is simplified by restrictingthe frequency characteristic of the differential signal detector 108.Generally, the frequency range in which a differential signal DIF withinthe servo control band can be detected is sufficient for the trackingcontrol system. Thus, an inexpensive amplifier with a narrow bandwidthcan be used as a differential input amplifier for detecting adifferential signal. An identification signal is in the form of asequence of pits, formed of intermittent grooves by modulation withdata. The differential signal DIF is in a smoothed waveform, because ofthe low-pass filtering, as shown in FIG. 12B.

The process in the reproduced differential signal processor 2 does notrequire the correction circuit 2 f used in the fourth embodiment, andthe two binarized signals can be treated in the same way as L2 and L3 inFIG. 11E and FIG. 11G.

The subsequent process is the same as in the third embodiment.

The same circuit configurations using the specific characteristics ofthe band-limited filter as is shown in this embodiment can be applied tothe second embodiment.

In the second to fifth embodiments described above, description has beengiven to the operation in which determination is made on the directionsof the displacement of the identification signal and the order of thedirections from the differential signal which is output from thetracking sensor, and the tracking polarity is determined accordingly. Itis also possible to reproduce, at the polarity information reproductioncircuit 4, the polarity information in the identification signal fromthe sum signal which is output from the tracking sensor, and use theresult in combination with the result of the tracking polaritydetermination obtained from the differential signal. By using both ofthe polarity information and the result of the tracking polaritydiscrimination obtained from the differential signal, more accurate andreliable tracking polarity setting can be realized.

The methods of detecting an identification signal and a track connectingpoint described in the above embodiments are, of course, only theexamples to illustrate the present invention. Similar functions may beimplemented by various circuit configurations, and the present inventionis not limited to the above embodiments.

What is claimed is:
 1. A method of reproducing data from an optical disk using an optical head which includes a multi-section photodetector, the optical disk having recording sectors of predetermined length and embossed pits for sector identification information, said method comprising: generating a differential signal based on signals produced by said multi-section photodetector as said optical head scans said embossed pits; reproducing sector identification information based on said differential signal using comparator circuitry having multiple threshold levels; producing a gating signal using a comparison with a gating signal threshold; and removing noise in said differential signal using said gating signal.
 2. The method of claim 1, wherein said embossed pits for sector identification are located at a boundary of neighboring tracks.
 3. The method of claim 2, wherein said optical disk includes land and groove track revolutions that are connected to form a single spiral of alternating land and groove tracks and said embossed pits are radially offset from a center of a groove track so as to overlap radially adjacent land and groove tracks.
 4. The method of claim 1, wherein said comparator circuitry includes first and second comparators that use first and second threshold levels, respectively, to binarize said differential signal. 